The purpose of this project is to provide new knowledge of how the cochlear nucleus processes the auditory information that it receives from the inner ear through the auditory nerve. We have in previous reports described findings indicating that the auditory nerve may use glutamate and/or aspartate as neurotransmitter in the cochlear nucleus. A logical outcome of these studies is our hypothesis that the enzymes glutaminase and aspartate aminotransferase may serve as markers for neurons that have glutamate and/or aspartate as neurotransmitter(s). To find evidence for or against this hypothesis and to get a better perspective of our findings on auditory nerve synapses we are pursuing immunocytochemical studies of the distribution of these enzymes in different parts of the nervous system. Small mammals (guinea pigs and rats) serve as research subjects; immunocytochemical techniques, light microscopy and electron microscopy are used. One paper on glutaminase in the auditory nerve has been submitted for publication; several manuscripts on both enzymes are in preparation. Previously mentioned electron microscopical studies of the development of auditory nerve synapses in the cochlear nucleus of the rat have been completed and have led to the publication of three papers. Our in vitro studies of auditory nerve synapses in the cochlear nucleus have been continued. Chamber mounted slices of the brainstem of mice have been prepared, drugs have been applied to synapses, either via fluid in the chamber as bath application, or through microiontophoresis. Slices containing the hippocampus of the mouse have been used for testing the parameters of the experiments. Such control experiments have led to interesting findings on potentiation in the hippocampus; results are being submitted for publication. Manuscripts on auditory nerve synapses are in preparation.